Bangkok is a massive city and there are a variety things to do. There is no optimum place to stay but the location of the Pentafield City Residence is as good as any in the city. There is the nearby On Nut BTS station which connects the city. But get the Grab app. You very quickly get a cab or bike to take you very cheaply anywhere in the city. The apartment is very comfortable and has the essential air con. The place is clean and the staff are very helpful. I had a problem with the shower which was solved within minutes but above all I appreciated the value for money of my stay.